The third generation wideband code division multiple access (3G W-CDMA) systems use power control as a link adaptation method. Dynamic power control is applied for dedicated physical channels (DPCHs), such that the transmit power of the DPCHs is adjusted to achieve a quality of service (QoS) with a minimum transmit power level, thus limiting the interference level within the system. The transmit power control of DPCHs is typically divided into two processes operating in parallel: inner loop power control (ILPC) and outer loop power control (OLPC). The ILPC algorithm controls transmit power to keep the received signal to interference ratio (SIR) of each DPCH as close as possible to a target SIR. The OLPC algorithm controls the target SIR per coded composite transport channel (CCTrCH), to keep the received quality as close as possible to a target quality. In other words, the output of the OLPC is an updated target SIR used for the ILPC.
A CCTrCH can be composed of multiple transport channels (TrCHs) and the block error rate (BLER) of each TrCH is specified separately. All TrCHs within the CCTrCH are controlled simultaneously by a transmit power control (TPC) command of the ILPC. Therefore, the OLPC must select a target SIR value sufficient to meet all of the individual TrCH BLER requirements.
The OLPC algorithms would initially set a target SIR according to the required target quality for a given service, such as BLER, using a fixed mapping between BLER and SIR, assuming a most plausible channel condition. However, the actual mapping from a target BLER to a target SIR may vary by a large amount depending on the channel conditions, especially at very low BLER. The OLPC is typically implemented based on the cyclic redundancy check (CRC) for a reference TrCH. Because of this, it often takes a long time to converge to the required target SIR for the low BLER whenever the channel conditions vary significantly, leading to degrading the performance of the entire power control algorithm. Accordingly, the OLPC selects a TrCH with the highest BLER and the shortest transmission time interval (TTI) within the CCTrCH as the reference channel. This result allows the OLPC to quickly reach the steady state, because errors will occur more frequently, enabling corrections to be made faster.
The rate matching attributes could be selected such that all TrCHs within the CCTrCH are balanced with respect to the desired target BLER assuming a scenario of the channel conditions (e.g., the best case of additive white Gaussian noise (AWGN), a worst case of WG4 case 1, or the average of all channel conditions). However, the rate matching parameters required will change with the channel conditions. For example, as shown in FIG. 1, if the rate matching parameters are selected with respect to a best channel condition of the AWGN channel, then the worst case scenarios will not meet the BLER qualities for the non-reference TrCHs. Whereas, if the rate matching parameters are selected with respect to a worst case of WG4 case 1, the non-worst case scenarios will achieve better than necessary BLERs for the non-reference TrCHs, which implies a loss of capacity. Moreover, the wireless transmit/receive unit (WTRU) will generally not know the reference channel condition for the rate matching in the radio network controller (RNC).
It is desirable to select the reference TrCH to better achieve all target BLERs in differing channel conditions.